Finally, we turn our attention to the atomic absorption line Ti i 6556.06 Å,
which is present in our medium-resolution spectra
(Figs. REF  and REF ) and has had a
stable position between the years 2009 and 2020 with a radial velocity
of \(+75\pm 2\)  km s\(^{-1}\)  and a full width at the continuum level of 85 km s\(^{-1}\) .
When comparing the Ti i profile
in our spectra with profiles of Ti i lines (6556.06 Å line among them)
in higher resolution spectra (see Fig. 3 panel c in [1]})
it is clear that the line profiles are
asymmetric, displaying a clear blue wing or blend. This asymmetry,
when fitting the entire profile in our significantly lower resolution data
with a single Gaussian, results in a systematic underestimation of the
line's radial velocity. Figure 3 of [1]} clearly shows that the real radial velocity of the Ti i line has a value
closer to +90 km s\(^{-1}\) .
A similar narrow velocity
component of \(86-87\)  km s\(^{-1}\)  has been found in the lines of the CO fundamental and first
overtone bands [3]} and in a number of atomic lines and high-excitation
molecular bands [4]}, and has been interpreted by these authors as infall. In
particular the lines of V i [4]} display only this
red-most velocity component, just as our Ti i 6556 Å line. Considering that in the cooler
envelope (or wind) these atoms are completely bound in the molecules TiO and VO, the absorption lines
of atomic Ti i and V i must arise in a hotter region in (or close to) the stellar
photosphere. Support for this interpretation comes from the fact that the excitation potential of
the lower level of the Ti i 6556 Å transition is 1.46 eV, whereas most of the other
atomic lines observable in the optical spectrum of V838 Mon with wind-modified profiles have lower
excitation potentials [1]}. In addition, [7]}
have measured in the 2020 SALT high-resolution spectrum of V838 Mon the absorption components
with heliocentric velocity of +85 km s\(^{-1}\)  in several lines from highly excited
states. These pieces of evidence and
the persistence of this absorption line
[4]}
for more than 15 years speaks against an interpretation as matter infall or stellar contraction: a contraction with a constant velocity of 16 km s\(^{-1}\)  over a time span of 15 years
would mean that the material has travelled a distance of more than \(10^{4}\,R_{}\) .
[9]} reported on a possible contraction of the SG's radius by
\(\sim 40\%\)  from about \(1200\,R_{}\)  to about \(750\,R_{}\)  within a ten-year period. Such a
contraction causes a red-shifted velocity of just \(\sim 1\)  km s\(^{-1}\) .
It is also worth mentioning
that starting from the year 2002 all the P Cygni profiles measured in the spectrum of V838 Mon have
had emission peaks at heliocentric velocities \(80-100\)  km s\(^{-1}\)  [10]}, [11]}, [7]}, and under the assumption of spherical winds, the
position of the emission peak indicates the radial velocity of the star.
We note here that in the light of the recent ALMA observations [7]},
which resolve the position
of both components in V838 Mon, it is clear that the maximum flux emission
is located at the position of the RSG (see their Fig. 3).
Therefore, the above-mentioned radial velocity
represents the velocity of the RSG, rather than the true barycentric (i.e. systemic) velocity of the system.
